Celiac disease is a complex intestinal inflammatory disorder with villous atrophy induced by dietary gluten in HLA-DQ2 or HLA-DQ8 individuals. The disease is the 'tip of an iceberg' including a larger subclinical population with various aspects of dysregulation in response to gluten. Immunological abnormalities associated with gluten uptake include (1) chronic upregulation of IL-15 in the epithelium and lamina propria, (2) massive expansion of natural killer-like intraepithelial cytotoxic lymphocytes (IE-CTL), (3) DQ2 or DQ8-restricted anti- gluten CD4 T cells secreting IFNg? in the lamina propria and (4) signature antibodies against gluten and the tissue transglutaminase (TTG) that binds and deamidates gluten. Villous atrophy may depend on the anti- gluten IFNg?+ CD4 T cell response, the expansion of IE-CTL and the overexpression of IL-15, but the precise links between these effector mechanisms remain unclear. The overarching aim of this proposal will be to model and investigate in vivo the consequences of chronic IL-15 expression using established transgenic systems expressing IL-15 at levels comparable to those observed in disease, and dissecting expression in the intestinal epithelium (villin promoter, V-IL15tg) and outside the epithelium in the lamina propria DC (minimal MHC class I Dd promoter, Dd-IL15tg). The conclusions will then be tested against a cohort of relatives of celiac patients where these immunological abnormalities naturally segregate. The ultimate goal is to combine DQ8 and IL-15 to model the histopathological stages of celiac disease. Specific aim 1, will analyze the impact of IL-15 on the breakdown of oral tolerance to ingested gluten; Specific Aim 2 will analyze the role of IL-15 in the acquisition of a natural killer phenotype by intraepithelial lymphocytes and the development of villous atrophy; and Specific Aim 3, will analyze in human studies the link between IL-15, anti-gluten adaptive immunity and natural killer transformation of intraepithelial lymphocytes. Collectively, these studies will not only provide new insights into the pathogenesis of celiac disease and the major impact of dysregulated IL-15 expression but also, importantly, will guide and refine new generation animal models. Because a strict lifelong gluten-free diet imposes tremendous constraints on patients, such models are long overdue to test alternative therapies that will be developed in the near future.